Bidirectional solenoid driving device



Feb. 18, 1969 E. R. sroDDARb 3,427,891

BIDIRECTIONAL SOLENOID DRIVING DEVICE Filed Au 23, 1966 Sheet I of 2 FIG. 1

INVENTOR ERNEST R. STODDARD WMMWM ATTORNEY Feb. 18, 1969 E. R. STODDARD 3,427,891

BIDIRECTIONAL SOLENOID DRIVING DEVICE Filed Aug. 23. 1966 Sheet 2 of 2 FIG. 2

INVENTOIR ERNEST R. STODDARD gg/m4! WM ATTORNEY United States Patent 3,427,891 BIDIRECTIONAL SOLENOID DRIVING DEVICE Ernest R. Stoddard, 89 Knollwood Drive, Wolcott, Conn. 06716 Filed Aug. 23, 1966, Ser. No. 574,430 US. Cl. 74-142 Claims Int. Cl. F16h 27/10, 31/00 ABSTRACT OF THE DISCLOSURE A bidirectional impulse stepping device having a first coil operating an armature which controls a first pawl to move a star wheel in one direction at least one-half a step. A resiliently biased second pawl moves the wheel in the same direction the remaining portion of the step when the first pawl is retracted. A second coil controls a second armature which in turn controls a third pawl to engage the star wheel and move it in the reverse direction at least one-half a step. The second pawl engages the star wheel when the third pawl is retracted to continue the motion begun by the third pawl to complete the movernent of the star wheel one full step. Thus the star wheel may be rotated both clockwise and counterclockwise and in either case the second pawl changes part of the motive power to move the wheel part of a step.

This invention relates to an actuating mechanism comprising solenoids and means to translate the armature motion of the solenoids into step-wise rotation of a shaft in either direction.

The actuating mechanism of the present invention includes a shaft, which is to be rotated with a stepwise motion, a star gear on the shaft, and two pawls, one of which normally engages the gear on one side of the shaft and the other of which engages the gear on the other side and is connected to the armature of a solenoid to be pivoted back and forth as the latter is repeatedly energized. The second pawl only makes contact with the gear when the solenoid is actuated to move the armature in one of its two directions and engages the gear to apply pressure having a tangential component, thereby causing the gear to rotate in one direction or the other, depending upon whether the force applied by the second pawl pushes the gear either clockwise or counterclockwise. The first pawl maybe lifted out of contact with the gear by means attached to the armature, or it may be subjected to a resilient force that presses it against the gear and can be overcome by the stronger pressure of the second pawl. A second solenoid and armature to which a third pawl is attached may be provided to engage the gear on the same general side as the second pawl, the only difference being that, if the second pawl is placed to apply pressure to rotate the gear clockwise, the third pawl will be placed to rotate the gear counterclockwise.

The invention will be described in greater detail in the following specification together with the drawings in which:

FIG. 1 is a plan view of a bidirectional solenoidoperated drive unit constructed according to the invention;

FIG. 2 is a side view of the unit of FIG. 1 with one of the frame plates removed to show the arrangement of the solenoids and pawls.

The term bidirectional as applied to the drive unit of FIG. 1, which may be called a stepper module, or motor, refers to the fact that the output shaft 11 of the unit can be driven either clockwise or counterclockwise. The two directions of rotation, for the sake of clarity of description, refer to the direction of rotation of the shaft 11 as viewed from the right hand-end. A gear 12, normally in the form of a star, or ratchet, having symmetrical, straight-sided teeth, is attached firmly to the shaft and is actuated by ice three pawls 13-15, which, together with their associated operating mechanisms, may be referred to hereinafter as clockwise and counterclockwise pawls, respectively, be-

cause of the direction of rotation that they impart to the shaft 11. The shaft is rotatably supported in two frame members 16 and 18 and extends through the frame member 16 for connection to any device that is to be driven by the stepper module.

The pawls 13-15 are all pivotally supported on a common shaft 19, which may be referred to as the armature shaft, supported in the frame members 16 and 18. The center pawl, which may also be referred to as the upper pawl since it happens to be uppermost in this embodiment, although in practice it is by no means limited to that position, is attached rigidly to a relatively long spacing journal 21 to be supported at the center of the shaft 19, while the clockwise pawl 13 and the counterclockwise pawl 15 are not directly attached to the shaft 19 in this embodiment but instead are rigidly attached to two armatures 22 and 23, respectively, which in turn are supported by separate journals on the shaft 19. The pawls 13 :and 15 may also be formed of the same pieces of metal as their respective armatures. The armature 22, which may also be referred to as the clockwise armature, has two journals 2'4 and 25 while the other armature 23, which is a mirror image of the armature 22 and may be referred to as the counterclockwise armature, has two journals 27 and 28 corresponding to the two journals 24 and 25. Between the journals 21 and 25 is a spacing washer 29 held in a groove 31 in the shaft 19 to keep the armature 22 from moving too far to the right and the journal 21 from moving too far to the left. On each side of the spacing washer 29 are two thrust washers 32 to minimize friction. A similar washer arrangement comprising a spacing washer 33 and two thrust washers 34 is located between the journal 21 and the journal 28 with the spacing washer 33 held in place by a groove 36 in the shaft 19. The armature 22 is actuated by a coil 37 mounted on a ferromagnetically soft core 38 staked or otherwise affixed to a ferromagnetically soft frame 39, which may be made of cold rolled steel or the like. The armature 22 is normally held away from the core 38 by a spring 41, one end of which is atached either to the armature 22 or to the pawl 13 and the other end of which is hooked into an opening '42 in the frame 39.

The armature 23 is controlled by current flowing in a coil 43 having a central ferromagnetically soft core 44 rigidly attached to the frame 39, not only for good mechanical support but also to provide a low reluctance path through the core 44 to the frame 39. The armature 23 is pivoted away from the core 44 by the force of a spring '46, one end of which is attached either to the armature 23 or to the pawl 15 and the other end of which is threaded through an opening 47 in the frame 39.

FIG. 2 is an end view of the stepper module of FIG. 1 but with the frame member 18 removed. Thus FIG. 2 shows the armature 22, coil 37, and core 38 but not the corresponding armature 23, coil 43, and core 44, which are directly behind the elements shown. FIG. 2 does show the shaft 19 on which both armatures 22 and 23 as well as the pawls 1315 pivot. The shaft 19 is positioned with respect to the coils 37 and 43 by means of two armature support sections 48 and 49, of which only the support section 48 is shown in-FIG. 2. Both of these support sections are attached by relatively narrow necks to a flange bent from one edge of an upright section 38a of the base 38, only the neck 50 and the flange 51 being shown in FIG. 2. One purpose of the narrow necks is to permit a small adjustment to be made in the location of the support sections relative to the coils 37 and 43 to align the armatures 22 and 23. The flange 51 has a tapped hole 55 to permit it to be bolted to the frame member 18, and there is a similar flange, which is not shown in FIG. 2, which is attached to the frame member 16.

FIG. 2 shows the relative positions of the tips of the three pawls 13-15 in their respective positions when no current is applied to either of the coils 37 or 43. The tip 14a of the upper pawl 14 normally rests on the gear 12 in a plane indicated in this view by the line 52, which is a radial line through the shaft 11 and the gear 12. The force pressing the tip 14a against the gear 12 is provided by a spring 54, one end of which is hooked over a bar 56 that passes through and is rigidly attached to the pawl 14, and the other end of which is hooked through a small hole 57 in a tongue 39a of the frame 39. The tip 13a of the pawl 13 extends beyond the line 52 and therefore beyond the tip 14a of the pawl 14 so that when the coil 37 is energized, the magnetic field produced by it will attract the armature 22 to the core 38 and will pivot the armature about the shaft 19, bringing the tip 13a of the pawl 13 into contact with one of the teeth of the star gear 12 beyond the center line 52. As a result the gear 12 will tend to rotate in the direction of the arrow 53, provided there is not too much obstruction from the tip 14a due to the force of the spring 54. The obstruction or interference furnished by the tip 14a can be eliminated by the provision of an adjustment screw 58 in the armature 22 which may be brought to bear upon the bar 56. Since this force is applied to one side of the central plane of the pawl 14, it tends to rotate the pawl about an axis perpendicular to the axis of the shaft 19, and this is one of the reasons why the spacing journal 21 must be relatively long, extending almost the full distance between the armatures 22 and 23. The adjustment screw 58 is held in a threaded hole 59 in the armature 22 and is maintained in place by a locknut 61. Because of the engagement between the screw 58 and the bar 56, pivoting of the armature 22 about the shaft 19 in response to current in the coil 37, which causes the tip 13a to move toward the star gear 12, simultaneously pivots the pawl 14 away from the star gear. The adjustment of the screw 58 is preferably such as to cause the tip 14a to move out of the path of motion of the star gear 12 just as the tip 13a reaches a position in which it starts to drive the star gear forward.

The distance from the center of the shaft 19 to the pawl tip 13a is greater than the distance from the center of the shaft 19 to the center of the shaft 11 and thus the pawl tip 13a may be said to engage the star gear 12 beyond the center plane represented by the line 52. The tip a of the other pawl 15, on the other hand, engages the star gear 12 on the same side of a central plane passing through line 52 as the shaft 19, thus producing a force that tends to rotate the gear 12 in the direction of the arrow 62. This direction is opposite to the direction that the pawl 14 must pivot for its tip 14a to move out of the way of the teeth of the gear 12 as the latter is rotated by the pawl 15. When the pawl 13 rotates the gear 12 in the direction of the arrow 53, the gear is turning in the same relative direction of rotation as the pawl 14 must pivot in moving out of the way, and the pawl 14 produces a greater interference with rotation of the gear 12 than when the gear is rotated in the direction of the arrow 62. The difference in force required to rotate the gear 12 in the two directions indicated by the arrows 53 and 62 may be such that, although the adjustment screw 58 is required for the armature 22, the adjustment screw 63 on the armature 23 may be eliminated. In addition to the fact that the gear 12 rotates more easily when it is turning in the opposite direction from the direction of pivoting of the pawl 14 than when it is turning in the same direction as the direction of the pivoting of the pawl 14, the pawl 15 has a shorter lever arm than the pawl 13 and thus, for the same amount of force produced by the coils 37 and 43 produces a higher torque to act upon the gear 12, which further minimizes the necessity for having the adjustment screw 63 to raise the pawl 14 by applying pressure beneath the bar 56.

In the operation of the stepper module, pulses of current will normally be applied to one or the other of the coils 37 and 43 alternately. This does not means that after the coil 37 has been energized for one pulse the next pulse must energize the coil 43; all that it means is that both the coil 37 and the coil 43 cannot be energized simultaneously. In practice it may frequently occur that one of the coils, for example the coil 43, will be energized repetitively by a series of a current pulses, and each time it is energized by one of these pulses, the armature 23 will be pivoted and the pawl 15 will drive the gear 12 and the shaft 11 one step in the appropriate direction. All this while, the coil 37 may be dormant, but at a later period thecoil 37 may be energized by a series of pulses while the coil 43 remains dormant.

In energizing the coils to actuate the armatures and thereby drive the gear 12 in one direction or the other, the angle through which th gear 12 and the shaft .11 are rotated by each complete movement of one of the armatures, for example the armature 23, must be at least enough to move the gear :12 in the appropriate direction the space of one tooth. To be specific, in the present embodiment the gear 12 has ten teeth as may be seen in FIG. 2, which means that it rotates 36 each step. Where the teeth are symmetrical, as they are in the embodiment shown in FIG. 2, the rotation produced by either of the pawls 13 or 15 must be sufficient to move the apex of the appropriate one of the teeth adjacent to the tip 14a of the pawl 14 far enough so that when the driving pawl, either 13 or 15, is disengaged from the gear, the spring 54 will pull the pawl 14 back into full mesh with the gear 12 but in a space between the next pair of teeth, either the teeth spaced in the clockwise direction or in the counterclockwise direction. Where the sides of the tip 14a are substantially straight and have an included angle substantially equal to the angle between adjacent sides of adjacent teeth of the gear 12, and the tip 14a moves in a substantially radial direction along the plane indicated by the line 52, the pawls 13 and .15 must rotate the gear 12 through an angle equal to at least half of the angle between adjacent teeth of the gear, that is, in the present embodiment, through an angle of at least 18". Where the tips 13a and 15a of the pawls 13 and 15, respectively, are rigid, it will be impossible for the gear 12 to be rotated more than the angle between successive teeth each time one of the pawls .13 or 15 is actuated. This places a maximum limit on the required amount of pivotal movement of the pawls 13 and 15 and consequently of the armatures 22 and 23. In order to set the armatures for optimum efiiciency, in which they would move the smallest distance to achieve the necessary stepping motion, a bar 66 may be placed above the armatures between the frame members -16 and 18 and provided with adjustment members in the form of screws 67 and 68 having locknuts 6'9 and 70, respectively. The screws 67 and 68 may then be moved in or out to set the limit of movement of the armatures 22 and 23 away from the respective cores 38 and 44.

While this invention has been described in terms of a specific embodiment it will be understood by those skilled in the art that modifications may be made therein within the scope of the following claims without departing from the true scope of the invention.

What is claimed is:

1. A bidirectional stepper module comprising: a first coil; an armature actuated by the magnetic field of said coil; a first pawl actuated by said armature; a second pawl; a gear; said first and second pawls having first and second tips, respectively, positioned to engage said gear; resilient means biasing said second pawl normally into engagement with said gear, said first pawl being normally resiliently biased away from said gear and being movable to engage said gear along a nonradial direction to rotate said gear through a first predetermined angle, said resilient means forcing the tip of said second pawl into engagement with said gear to rotate said gear through a second predetermined angle in the same direction as said first predetermined angle after said first pawl disengages from said gear, said first and second predetermined angles being at least equal to the angle between adjacent teeth on said gear.

2. The stepper module of claim t1 in which said first pawl is a rigid member mounted to pivot about an axis with said first tip at a fixed distance from said axis, said second pawl is a rigid member mounted to pivot about the same axis with said second tip at a fixed distance from said axis, and the sum of said first and second predetermined angle is at least equal to the angle between adjacent teeth on said gear.

3. The stepper module of claim 1 in which said gear is a star gear and said teeth are symmetrical and said first predetermined angle is at least equal to one-half the spacing between adjacent teeth of said star gear.

4. The stepper module in claim 3 in which the sides of each of said teeth of said gear are substantially straight and said second tip has straight sides engaging said teeth, the angle between said straight sides being substantially equal to the angle between adjacent surfaces on two adjacent one of said teeth.

5. The stepper module of claim 1 comprising, in addition: an adjustable engagement structure on said armature to engage said second pawl when said coil is actuated to lift said second pawl away from engagement with said gear as said first pawl comes into engagement with said gear.

6. The stepper module of claim 5 comprising, in addition: locking means to look said engagement means in a selected position to engage said second pawl after said armature has moved a predetermined distance.

7. The stepper module of claim 5 comprising, in addition: a common shaft on which said armature and first pawl are pivotally mounted and on which said second pawl is pivotally mounted alongside said armature; and a transverse pin on said second pa-wl extending over said engagement means on said armature to be engaged thereby to lift said second pawl.

8. The stepper module of claim 7 comprising, in addition: an elongated journal on said shaft, said second pawl being rigidly attached to said elongated journal to limit rotation of said second pawl about an axis at an angle to said common shaft.

'9. The stepper module of claim 1 comprising, in addition: a second coil; a second armature actuated by the magnetic field of said second coil; a third pawl actuated by said second armature and normally biased away from engagement with said gear but movable to engage said gear along a second nonradial direction to rotate said gear through a third predetermined angle in the opposite direction from said first predetermined angle.

10. The stepper module of claim 9 in which said second pawl engages said gear substantially along a radial line through said gear.

11. The stepper module of claim 10 in which said first and third pawls engage said gear on the opposite side of said gear from said second pawl.

12. The stepper module of claim 11 in which said first and third pawls engage said gear on opposite sides of a plane including the radial line along which said second pawl engages said gear.

13. The stepper module of claim 9 comprising, in addition: a shaft, said first-named armature and said second armature both being pivotally mounted on said shaft and said second pawl also being pivotally mounted on said shaft between said armature and said second armature.

14. The stepper module of claim 13 comprising, in addition: engagement means on said first-named armature to engage said second pawl to lift said second pawl out of engagement with said gear when said first-named armature moves said first pawl into engagement with said gear, said first pawl engaging said gear .along a nonradial direction to rotate said gear in the same relative direction as said second pawl pivots in moving out of engagement with said gear.

;15. The stepper module of claim 14 comprising, in addition: a second engagement means on said second armature to engage said second pawl and to move said second pawl out of engagement with said gear when said second armature is actuated to move said third pawl into engagement with said gear to rotate said gear in a direction opposite the direction that said second pawl pivots in moving out of engagement with said gear.

References Cited UNITED STATES PATENTS 2,377,583 6/1945 Smith 74-142 3,142,188 7/1964 Miller 74-142 3,148,815 9/1964 Jung 74-142 3,201,659 8/ 1965 Poulton et a1. 335-273 FRED C. MATTERN, JR., Primary Examiner. W. S. RATLIFF, 1a., Assistant Examiner. 

